Publications

2005

• Plasmon channels in the electronic relaxation of diamond under high-order harmonics femtosecond irradiation.
  
  • Belsky Andrei
  • Esnouf Stéphane
  • Garnov Serguei V.
  • Gaudin Jérôme
  • Geoffroy Ghita
  • Guizard Stéphane
  • Klimentov Serguei M.
  • Martin Patrick
  • Olevano Valério
  • Petite Guillaume
  • Pivovarov Pavel A.
  Laser Physics, MAIK Nauka/Interperiodica, 2005, Letters 2, pp.292-296. We used high order harmonics of a femtosecond titanium-doped sapphire system (pulse duration 25 fs) to realise Ultraviolet Photoelectron Spectroscopy (UPS) measurements on diamond. The UPS spectra were measured for harmonics in the range 13 to 27. We also made ab initio calculations of the electronic lifetime of conduction electrons in the energy range produced in the UPS experiment. Such calculations show that the lifetime suddenly diminishes when the conduction electron energy reaches the plasmon energy, whereas the UPS spectra show evidence in this range of a strong relaxation mechanism with an increased production of low energy secondary electrons. We propose that in this case the electronic relaxation proceeds in two steps : excitation of a plasmon by the high energy electron, the latter decaying into individual electron-hole pairs, as in the case of metals. This process is observed for the first time in an insulator and, on account of its high efficiency, should be introduced in the models of laser breakdown under high intensity. (10.1002/lapl.200510001)
  DOI : 10.1002/lapl.200510001
• Magnetic structure of beta-ErD2: Long-range and short-range order from powder neutron diffraction
  
  • Vajda P.
  • André G.
  • Udovic T.J.
  • Erwin R.W.
  • Huang Q. S.
  Physical Review B: Condensed Matter and Materials Physics (1998-2015), American Physical Society, 2005, 71, pp.054419. Two parallel neutron powder diffraction investigations were performed on different specimens of ErD2 at the LLB (CEN Saclay) and at NIST for the determination of its magnetic structure. It comprises, below Tn=2.23 K, two coexisting sinusoidally modulated antiferromagnetic (AF) configurations, M' and M'', with the respective incommensurate propagation vectors, k'=(0.275,0.275,0.750), together with its third harmonic 3k', and k''=(0.120,0.120,0.750). Contrary to other heavy rare-earth dideuterides, no commensurate AF configuration could be detected down to 120 mK. On the other hand, similar to earlier observations on HoD2 and TbD2, magnetic short range order (SRO shows up near 1.5 K in ErD2 after the disappearance of certain M'' lines. This SRO seems to correlate with the hexagonal gamma-phase of the trideuterite and suggests an electronic phase separation with memory effects
• Raman and EPR studies of ß-irradiated oxide glasses: The effect of iron concentration
  
  • Olivier F.Y.
  • Boizot B.
  • Ghaleb D.
  • Petite G.
  Journal of Non-Crystalline Solids, Elsevier, 2005, 351, pp.1061. The study of iron concentration on the oxide glass structure has shown evidence of depolymerization of the vitreous network with increasing iron content and especially with Fe2+ amount for all types of glass. For all glass compositions studied, we observe by EPR a blockage of defects creation processes under beta irradiation for glasses doped with more than 1 wt% of Fe2O3. Reduction processes of Fe3+ under irradiation is also detected. Moreover for sodalime glass samples, beta irradiation induces depolymerization, in opposite of what was expected and observed for other glasses. Anyway, adding iron up to 4 wt% Fe2O3 always diminishes the beta irradiation effects. This has been linked to the observed iron reduction and to the ability of iron, maybe coupled with charge trapping processes to consume excitons
• Multiple superconducting phases in heavy fermion superconductors
  
  • Matsuda Y.
  • Izawa K.
  • Watanabe T.
  • Kasahara Y.
  • Nakajima Y.
  • Sakakibara T.
  • van Der Beek C.J.
  • Nohara M.
  • Hanaguri T.
  • Takagi H.
  • Goryo J.
  • Maki K.
  • Thalmeier P.
  • Osaki S.
  • Sugawara H.
  • Sato H.
  • Shishido H.
  • Settai R.
  • Onuki Y.
  Journal of Physics and Chemistry of Solids, Elsevier, 2005, 66, pp.1365. We show that in recently discovered heavy fermion superconductors, quasi two-dimensional CeCoIn5 and skutterudite PrOs4Sb12, multiple superconducting phases with different symmetries manifest themselves below T-c. The ultrasound velocity measurements revealed that in CeCoIn5 the Fulde-Ferrel-Larkin-Ovchinikov phase, in which the order parameter is spatially modulated and has planar nodes aligned perpendicular to the vortices, appears at low temperature and high field. The angle resolved magnetothermal transport measurements revealed that in PrOs4Sb12 a novel change in the symmetry of the superconducting gap function occurs deep inside the superconducting state. These results open up a new realm for the study of the superconductivity with multiple phases
• Conductance in multiwall carbon nanotubes and semiconductor nanowires
  
  • Dayen J.F.
  • Wade T.L.
  • Konczykowski M.
  • Wegrowe J.E.
  • Hoffer X.
  Physical Review B: Condensed Matter and Materials Physics (1998-2015), American Physical Society, 2005, 7207, pp.3402. Electronic transport in an ensemble of multiwall carbon nanotubes and semiconductor nanowires was compared. The nanotubes and nanowires are obtained by template synthesis and are contacted in a current perpendicular to the plane geometry by using different methods. In all cases, the nonohmic behavior of the conductance, the so-called zero-bias anomaly, shows a temperature dependence that scales with the voltage dependence. This robust scaling law describes the conductance G(V,T) by a single coefficient alpha. A universal behavior as a function of alpha is found for all samples. Magnetoconductance measurements furthermore show that the conduction regime is weak localization. The observed behavior can be understood in terms of the Coulomb blockade theory, providing that a single tunnel barrier is present. This hypothetical tunnel barrier would have a resistance of the order of 2500 Omega and a typical energy of about 40 meV for all samples
• Nucleation and growth of single wall carbon nanotubes
  
  • Beuneu Francois
  Solid State Communications, Elsevier, 2005, 136, pp.462. The nucleation and growth of single wall carbon nanotubes from a carbon-saturated catalytic particle surrounded by a single sheet of graphene is described qualitatively by using a very restricted number of elementary processes, namely Stone-Wales defects and carbon bi-interstitials. Energies of the different configurations are estimated by using a Tersoff energy minimization scheme. Such a description is compatible with a broad variety of size or helicity of the tubes. Several mechanisms of growth of the embryos are considered: one of them is made more favourable when the tubes embryos are arranged in an hexagonal network in the graphene plane. All the proposed mechanisms can be indefinitely repeated for the growth of the nanotubes. (10.1016/j.ssc.2005.09.007)
  DOI : 10.1016/j.ssc.2005.09.007
• Energy dependence of the exchange-correlation kernel of time-dependent density functional theory: A simple model for solids
  
  • Botti Silvana
  • Fourreau A.
  • Nguyen F.
  • Renault Y.-O.
  • Sottile F.
  • Reining L.
  Physical Review B: Condensed Matter and Materials Physics (1998-2015), American Physical Society, 2005, 72, pp.125203. Time-dependent density functional theory faces an important problem when it comes to extended systems: The long-range component of the exchange-correlation kernel fxc is completely absent from local density or generalized gradient approximations, but it is believed to be present in the “exact” fxc . Several attempts have been made to solve this issue, the simplest of them being the use of a model static long-range kernel of the form −αstatic∕q2 . In this paper, we propose and motivate a dynamical extension of this model of the form −(α+βω2)∕q2 . The dynamical model is then used to calculate the dielectric function of a large variety of semiconductors and insulators. The absorption spectra of large gap insulators are remarkably improved with respect to calculations where the kernel is taken to be static. This approach is valid also for energies in the range of plasmons, and hence it yields, e.g., good electron energy loss spectra. Finally, we present some simple theoretical arguments that relate the parameters of the model to physical quantities, like the dielectric constant and the plasmon frequency. (10.1103/PhysRevB.72.125203)
  DOI : 10.1103/PhysRevB.72.125203
• Growth dynamics of hydrogenated silicon nanoparticles under realistic conditions of a plasma reactor
  
  • Vach H.
  • Brulin Q.
  • Chaâbane N.
  • Novikova T.
  • Roca I Cabarrocas Pere
  • Kalache B.
  • Hassouni K.
  • Botti Silvana
  • Reining Lucia
  Computational Materials Science, Elsevier, 2005, 35, pp.216-222. We present results of an extensive numerical study that was motivated by the experimental problem to understand under which conditions SinHm nanoparticles deposited by plasma enhanced chemical vapor deposition (PECVD) take an amorphous or a crystalline structure. A crystalline structure of those particles is crucial, for example, for the electrical properties and lifetime of polymorphous solar cells. First, we use a fluid dynamics model to characterize the experimentally employed silane plasma. The resulting relative densities for all plasma radicals, their temperatures, and their collision interval times are then used as input data for detailed semiempirical quantum molecular dynamics simulations. As a result the growth dynamics of nanometric hydrogenated silicon SinHm clusters is simulated starting out from the collision of individual SiHx radicals under the plasma conditions derived above. We demonstrate how the details of the plasma determine the amorphous or crystalline character of the forming nanoparticles. Finally, we show a preliminary absorption spectrum based on ab initio time-dependent DFT calculations for a crystalline Si10H16 cluster to demonstrate the possibility to monitor the cluster growth in situ. (10.1016/j.commatsci.2004.07.010)
  DOI : 10.1016/j.commatsci.2004.07.010
• Relationship between structure, segregation and electrical activity in grain boundaries
  
  • Lamzatouar A.
  • Palais Olivier
  • B. M. Hardouin Duparc O.
  • Thibault J.
  • Charaï A.
  Journal of Materials Science, Springer Verlag, 2005, 40, pp.3163-3167. Using the contactless microwave phase-shift technique (μ W-PS) and High Resolution Transmission Electron Microscopy (HRTEM), we show that the twist and mixed parts of a < 110 > Σ = 51(θ = 16.10∘) grain boundary in germanium (Ge) are electrically active. We also show that we can passivate the electrically active grain boundaries by sulfur segregation which has been studied by energy filtering HRTEM. Atomistic simulations show that the most favorable places for this segregation are the high energy sites of grain boundary
• The planar-to-tubular structural transition in boron clusters from optical absorption
  
  • A. L. Marques Miguel
  • Botti Silvana
  The Journal of Chemical Physics, American Institute of Physics, 2005, 123, pp.014310. The optical response of the lowest-energy isomers of the B20 family is calculated using time-dependent density-functional theory within a real-space, real-time scheme. Significant differences are found among the absorption spectra of the clusters studied. We show that these differences can be easily related to changes in the overall geometry. Optical spectroscopy is thus an efficient tool to characterize the planar-to-tubular structural transition, known to be present in these boron-based systems. (10.1063/1.1948386)
  DOI : 10.1063/1.1948386
• Deuterium trapping in sintered polished UO2 disks
  
  • Labrim H.
  • Barthe M.F.
  • Sauvage T.
  • Desgardin P.
  • Blondiaux G.
  • Corbel C.
  • Miserque F.
  • Piron J.P.
  Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, Elsevier, 2005, 240, pp.434. In this work we present deuterium analysis performed using the H-2(He-3, alpha)H-1 Nuclear Reaction Analysis method. Different sets of sintered polished uranium oxide disks have been investigated before and after annealing at 400 degrees C in ArD2 atmosphere. Heterogeneous lateral deuterium distributions have been found for all the ArD2 annealed UO2 disks. The average deuterium amount increases after annealing at 400 degrees C in ArD2 and decreases after a second annealing at 400 degrees C in vacuum whatever is the set of sintered polished uranium oxide disks
• Photoconductivité et photoémission de diamant(s) sous irradiation XUV femtoseconde
  
  • Gaudin J.
  • Geoffroy G.
  • Guizard S.
  • Esnouf S.
  • Olevano Valério
  • Petite G.
  • Klimentov S.M.
  • Pivovarov P.A.
  • Garnov S.V.
  • Carre B.
  • Martin P.
  • Belsky A.
  Journal de Physique IV Proceedings, EDP Sciences, 2005, 127, pp.131-138. En fonction de l'ordre de l'harmonique, on constate que le signal de PC augmente tout d'abord (harmoniques 9 à 13) puis diminue au delà. Si l'augmentation s'interprète aisément comme résultant de phénomènes de multiplication par collisions inélastiques, la diminution ultérieure n'a pas pour le moment d'explication. Les mesures de spectre de photoémission suggèrent un effet important de la relaxation par émission de plasmons. Enfin, nous avons réalisé le premier calcul ab-initio de la durée de vie des porteurs tenant compte des interactions électron-électron, à l'aide d'une approche de théorie quantique à plusieurs corps de type GW. Au voisinage du gap, on observe un comportement proche de celui d'un liquide de Fermi. A plus haute énergie on observe des déviations à ce comportement, provenant d'effets de structure de bande d'une part, et d'excitations de plasmons d'autre part
• Many-body perturbation theory using the density-functional concept: beyond the GW approximation
  
  • Bruneval Fabien
  • Sottile Francesco
  • Olevano Valério
  • del Sole Rodolfo
  • Reining Lucia
  Physical Review Letters, American Physical Society, 2005, 94, pp.186402. We propose an alternative formulation of Many-Body Perturbation Theory that uses the densityfunctional concept. Instead of the usual four-point integral equation for the polarizability, we obtain a two-point one, that leads to excellent optical absorption and energy loss spectra. The corresponding three-point vertex function and self-energy are then simply calculated via an integration, for any level of approximation. Moreover, we show the direct impact of this formulation on the timedependent density-functional theory. Numerical results for the band gap of bulk silicon and solid argon illustrate corrections beyond the GW approximation for the self-energy.
• Classical versus ab initio structural relaxation: electronic excitations and optical properties of Ge nanocrystals embedded in an SiC matrix
  
  • Cappellini G.
  • Weissker H-Ch
  • de Salvador D.
  • Furthmüller J.
  • Bechstedt F.
  • Satta G.
  • Casula F.
  • Colombo L.
  Journal of Physics: Condensed Matter, IOP Publishing [1989-....], 2005, 17, pp.643. We discuss and test a combined method to efficiently perform ground-state and excited-state calculations for relaxed structures using both a quantum first-principles approach and a classical molecular-dynamics scheme. We apply this method to calculate the ground state, the optical properties, and the electronic excitations of Ge nanoparticles embedded in a cubic SiC matrix. Classical molecular dynamics is used to relax the large-supercell system. First-principles quantum techniques are then used to calculate the electronic structure and, in turn, the electronic excitation and optical properties. The proposed procedure is tested with data resulting from a full first-principles scheme. The agreement is quantitatively discussed between the results after the two computational paths with respect to the structure, the optical properties, and the electronic excitations. The combined method is shown to be applicable to embedded nanocrystals in large simulation cells for which the first-principles treatment of the ionic relaxation is presently out of reach, whereas the electronic, optical and excitation properties can already be obtained ab initio. The errors incurred from the relaxed structure are found to be non-negligible but controllable
• Spin-Induced Forbidden Evanescent States in III-V Semiconductors
  
  • Rougemaille1 H.-J. Drouhin2 S. Richard3 G. Fishman3 And A. K. Schmid1 N.
  Physical Review Letters, American Physical Society, 2005, 95, pp.186406. Within the band gap of a semiconductor no electronic propagating states are allowed, but there exist evanescent states which govern charge transport such as tunneling. In this Letter, we address the issue of their spin dependence in III-V semiconductors. Taking into account the spin-orbit interaction, we treat the problem using a k p 14 14 Hamiltonian that we numerically compute for GaAs. Our results show that the removed spin degeneracy in the band gap can lead to giant energy splittings and induces forbidden zones in k space where evanescent states are suppressed. (10.1103/PhysRevLett.95.186406)
  DOI : 10.1103/PhysRevLett.95.186406
• On the problem of the correct interpretation of phason elasticity in quasicrystals
  
  • Coddens Gerrit
  , 2005. Recently Francoual et al. claimed to have observed the dynamics of long-wavelength phason fluctuations in i-AlPdMn quasicrystals. We will show that the data reported call for a more detailed development of the elasticity theory of Jaric and Nelsson in order to determine the nature of small phonon-like atomic displacements with a symmetry that follows the phason elastic constants.
• Wave propagation in highly inhomogeneous thin films : exactly solvable models
  
  • Petite Guillaume
  • Shvartsburg Alexander
  , 2005, pp.59890M-1. We present an exact treatment of wave propagation in some inhomogeneous thin films with highly space-dependent dielectric constant. It is based on a space transformation which replaces the physical space by the optical path. In the new space, the dispersion equation is that of a normal progressive wave. We will show that the dispersion properties of such films are plasma- or waveguide-like, the characteristic frequency being determined by the spatial characteristics of the dielectric constant's variations only. The theory is scalable, so that it can be applied in any wavelength range : optical, IR, radiofrequency, etc. depending only on the characteristic space scales. Several applications will be presented, concerning the reflection properties of such films (broadband anti-reflection, or dichroic coatings) or to the propagation and transmission through the film. We will show that depending on the type of space dependence, an incident wave can either propagate or tunnel through such films. We will investigate the behaviour of the light group-velocity and tunneling time inside or through such films. Though we can reproduce the phase-time saturation corresponding to the Hartman effect, analysis of the group velocity in the tunneling case shows no sign of superluminal propagation. A strong frequency dependence can be obtained in some situations, which allows to anticipate a strong reshaping of brodband laser pulses. (10.1117/12.632046)
  DOI : 10.1117/12.632046
• Characterization of swift heavy ion tracks in CaF2 by scanning force and transmission electron microscopy
  
  • Khalfaoui N.
  • Rotaru C.C.
  • Bouffard S.
  • Toulemonde M.
  • Stoquert J.P.
  • Haas F.
  • Trautmann C.
  • Jensen J.
  • Dunlop A.
  Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, Elsevier, 2005, 240, pp.819. Single crystals of fluorite (CaF2) were exposed to various swift heavy ions (Ca up to U) of energy 1-11.1 MeV per nucleon, covering a large range of electronic stopping power S-e between 4.6 and 35.5 keV/nm. The irradiated (I 1 1) cleaved surfaces were investigated by means of scanning force microscopy in tapping mode. Nanometric hillocks produced by the ion projectiles were analyzed in terms of creation efficiency E-eff, diameter and height values, and diameter-height correlation. Hillock formation appears with a low efficiency above a Se threshold of similar to 5 keV/nm. The mean height of these hillocks is approximately constant (similar to 1 nm) between 5 and 10 keV/nm and increases linearly with Se above 10 keV/nm reaching 12.5 nm for the largest Se value investigated. Similarly, the efficiency grows versus Se achieving 100% for S-e > 13 keV/nm where each projectile produces an individual hillock. Above 13 keV/nm, the hillock height and diameter are strongly correlated. The diameter was deduced by graphical deconvolution of the scanning-tip curvature that is determined experimentally for each set of measurements. In the entire Se regime, the mean diameter exhibits a constant value of similar to 13 nm, which is significantly larger than 6 nm wide tracks observed by transmission electron microscopy
• Electron emission from solids under electron irradiation: a Monte Carlo study
  
  • Hakala M.
  • Corbel C.
  • Nieminen R.M.
  Journal of Physics D: Applied Physics, IOP Publishing, 2005, 38, pp.711. We have implemented a Monte Carlo simulation method to study electron emission from solid surfaces under electron irradiation at energies of up to 100 keV. Calculations are performed for the yields and energy distributions of the emitted electrons in backscattering and transmission geometries for Al and Au metals. For transmission studies the film thicknesses range from a few nanometres to micrometres. The method is demonstrated to predict correctly the electron backscattering and transmission properties, and gives a qualitatively reasonable description of the low-energy (E < 50 eV) secondary electron emission. For the exit surface of thin films we predict a universal behaviour according to which the maximum low-energy secondary electron yield is obtained when similar to 50-70% of the incident electrons are transmitted through the film. This corresponds to film thicknesses of similar to 0.75 times the mean depth of penetration of the electron with the same kinetic energy in a bulk target
• Effect of self-consistency on quasiparticles in solids
  
  • Bruneval Fabien
  • Vast Nathalie
  • Reining Lucia
  Physical Review B: Condensed Matter and Materials Physics (1998-2015), American Physical Society, 2005, 74, pp.045102. We have evaluated the self-energy of solids within different self-consistent approximations, from bare and screened exchange to screened exchange plus Coulomb hole !COHSEX" and GW approximations. Our calculations for silicon, aluminum, and argon assess the quality of the local-density approximation !LDA" valence wave functions and density with respect to their GW counterparts. The LDA conduction wave functions are shown to be of significantly poorer quality, in particular for not highly symmetric points of the Brillouin zone. Comparing the different approaches we show that screened exchange alone is not reliable and we propose to combine a self-consistent COHSEX with a subsequent perturbative GW calculation that gives a reasonable estimate of the self-consistent GW results, at a much lower computational cost. The calculations are based on the pseudopotential method; they confirm its reliability.
• Modification of N-doped carbon induced by 30 MeV C60 ions
  
  • Wang Z.G.
  • Dunlop A.
  • Zhao Z.M.
  • Song Y.
  • Jin Y.F.
  • Zhang C.H.
  • Sun Y.M.
  • Liu J.
  Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, Elsevier, 2005, 230, pp.262. In the present work, 120 keV N-ion doped and 30 MeV C60 ion irradiated graphite-like-carbon samples were characterized by RBS, micro-FTIR, micro-Raman, XPS spectroscopy and the variation of the properties of the samples with the N-dopant and/or C60 irradiation fluence have been studied. The RBS spectra showed that C60 irradiation can induce a partial diffusion of N atoms to the surface and the amount of the diffused N atoms increases slightly with increasing C60 irradiation fluence. The FTIR and Raman spectra exhibit characteristic bands of carbon nitrogen bonds showing that the C and N atoms are chemically bonded. The amount of chemically bonded C and N atoms increases with increasing N-dopant. By deconvolution of the XPS spectra, the atomic concentration of N and C atoms were obtained and it was identified that the samples mainly consist of three phases, namely, C3N4, CNx and tetrahedral amorphous carbon. The effect of N-dopant and C60 irradiation fluence on the modification of the properties of the samples is also discussed.
• A brief introduction to the ABINIT software package
  
  • Gonze X.
  • Rignanese G.M.
  • Verstraete M.
  • Beuken J.M.
  • Pouillon Y.
  • Caracas R.
  • Jollet F.
  • Torrent M.
  • Zerah G.
  • Mikami M.
  • Ghosez P.
  • Veithen M.
  • Raty J.Y.
  • Olevano Valério
  • Bruneval F.
  • Reining L.
  • Godby R.
  • Onida G.
  • Hamann D.R.
  • Allan D.C.
  Zeitschrift für Kristallographie, De Gruyter, 2005, 220, pp.558. A brief introduction to the ABINIT software package is given. Available under a free software license, it allows to compute directly a large set of properties useful for solid state studies, including structural and elastic properties, prediction of phase (meta)stability or instability, specific heat and free energy, spectroscopic and vibrational properties. These are described, and corresponding applications are presented. The emphasis is also laid on its ease of use and extensive documentation, allowing newcomers to quickly step in